Cushioned swing circuit

ABSTRACT

Cushioned swing circuits sometimes have a restricted passage between the motor conduits to allow the implement controlled by the swing circuit to coast to a stop. However, opening and closing of the restricted passage was manually controlled, thereby requiring an additional manipulative step by the operator. The present cushioned swing circuit includes a cushion valve moveable to an open position to establish communication through vent line means when a pressure differential greater than a predetermined level is generated in one of the motor conduits connecting a directional control valve to a hydraulic motor. The cushion valve is retained in the open position for a predetermined limited time after the pressure differential drops below the predetermined level so that the inertia generated pressure in the circuit is dissipated through the vent line means. At the end of the predetermined limited time, the cushion valve is moved to the closed position blocking communication through the vent line means whereupon the circuit is hydraulically locked. The cushion valve is moved between the opened and closed positions automatically and requires no additional effort by the operator.

DESCRIPTION

1. Technical Field

This invention relates generally to a swing circuit for controlling theswinging movement of a boom for a backhoe or excavator and moreparticularly to a means for dissipating the inertial energy in thecircuit when movement of the boom is suddenly stopped.

2. Background Art

The position of a boom of a backhoe is commonly controlled by a pair ofbi-directional hydraulic cylinders or motors connected between a mainsupport frame and a boom support frame. The boom is swung in an arcuatepath about its pivotal connection to the main frame generally byextending one of the motors and retracting the other motor. The boomcontrol circuit is normally provided with a pair of line relief valvesand a pair of make-up valves connected to the respective conduitsconnecting the control valve to the hydraulic motors. The line reliefvalves function to vent fluid from one of the conduits when excessivepressure is generated therein while the make-up valves function toprovide make-up fluid to a conduit if it becomes cavitated.

One of the problems sometimes encountered therewith occurs when theswinging motion of the boom is abruptly stopped by moving thedirectional control valve to its neutral position and the inertialenergy of the boom and an implement supported thereby generates fluidpressure in one of the conduits sufficient to open the relief valvethereby allowing fluid to be expelled from that conduit. This results inthe other conduit being cavitated. While the make-up valves direct mostof the expelled fluid into the cavitated conduit some of the expelledfluid leaks past other valves in the system and not all of the expelledfluid is reclaimed such that a void is created on one side of thehydraulic motor. This void then allows the boom to rebound or bouncefrom side to side a small amount until the inertia energy is dissipated.This is a performance deficiency sometimes referred to as "boom wag".One approach to solving a similar boom wag problem in hydraulicexcavators is to interconnect the conduits through an orificed passageso that the high pressure fluid generated in the one conduit by theinertia of the boom is transmitted directly to the other conduit.However, heretofore the orificed passage was either open all the time orit had to be blocked by the operator manually initiating the closing ofa valve. If the orificed passage is open at all times, then the boom candrift if the backhoe is being operated on a side slope. If a manualactuated valve is employed, then the operator has an additional functionto perform.

The present invention is directed to overcoming one or more of theproblems as set forth above.

DISCLOSURE OF THE INVENTION

In one aspect of the present invention a cushioned swing circuitcomprises a bi-directional hydraulic motor, a directional control valve,first and second motor conduits individually connected to thedirectional control valve and to the opposite ends of the motor, ventline means connected to one of the first and second motor conduits, anda cushion valve connected to the vent line means and moveable between aclosed position blocking fluid flow through the vent line means and anopen position establishing fluid flow through the vent line means. Thecushion valve includes spring means for resiliently biasing the cushionvalve to the closed position. A means is provided for restricting fluidflow through the vent line means when the valve is in the open position.A flow restriction means disposed in one of the first and second motorconduits generates a pressure differential in the fluid therein whenfluid is flowing therethrough. A means is provided for moving thecushion valve to the open position when the pressure differntial exceedsa predetermined level. A means is provided for maintaining the cushionvalve in the open position for a predetermined limited time after thepressure differential drops below the preselected level.

The present invention provides a cushioned swing circuit which has acushion valve for controlling the communication of fluid through a ventline means connected to a first motor conduit. The cushion valve isnormally closed and is opened when a pressure differential above apredetermined level is generated in the second motor conduit by a flowrestriction means disposed in the second motor conduit. Thus, when thedirectional control valve is moved to a neutral fluid blocking position,the pressure generated in the first motor conduit by the inertial energyof the implement is dissipated through the vent line means. The fluidflow through the vent line means is restricted. In two embodiments, thevent line means is connected to the second conduit so that the inertiagenerated pressurized fluid expelled from the first motor conduit istransmitted directly to the second motor conduit. In a third embodiment,the pressurized fluid passes through the vent line means to a tank. Thecushion valve is retained in the open position for a predeterminedlimited time after the pressure differential drops below thepredetermined level. Such period of time is selected so that by the timethe boom comes to a stop, the cushion valve will have moved to a closedposition so that the boom is then hydraulically locked in the desiredposition. Thus, opening and closing of the cushion valve is automaticand does not require an additional function for the operator to perform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, and 3 are schematic representations of embodiments of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1, a first embodiment of a cushioned swing circuit10 controls fluid flow to and from a pair of bi-directional hydraulicmotors 11,12. The hydraulic motors of this embodiment are utilized forcontrolling the swinging motion of a rotatable mechanism such as a boom(not shown) of a backhoe and have their opposite ends suitablyinterconnected such that as the hydraulic motor 11 extends, thehydraulic motor 12 retracts and vice-versa. A directional control valve13 is connected to a pump 14 and to a tank 16 in the usual manner. Firstand second motor conduits 17,18 are individually connected to thedirectional control valve 13 and to the opposite ends of the hydraulicmotor 11. A pair of line relief valves 19 and a pair of make-up valves21 are suitably connected to the first and second motor conduit 17,18and to the tank 16 in the usual manner.

The directional control valve 13 is moveable between a neutral closedposition as shown and first and second operating positions. In theclosed position, the first and second motor conduits 17,18 are blockedfrom each other and from the pump 14 and the tank 16. Upward movement ofthe directional control valve 13, as viewed in the drawing, to the firstoperating position establishes communication between the pump 14 and thesecond motor conduit 18 and between the first motor conduit 17 and thetank 16. Conversely, moving the directional control valve downwardly tothe second operating position establishes communication between the pump14 and the first motor conduit 17 and between the second conduit 18 andthe tank 16.

A vent line means 22 has a first section 23 connected to the first motorconduit 17 and a second section 24 connected to the second motor conduit18. A cushion valve 26 is disposed between and connected to the firstand second sections 23,24 of the vent line means 22. The cushion valveis a three-position valve and is shown in a centered closed positionblocking fluid flow through the vent line means 22. The cushion valve ismoveable either leftwardly or rightwardly from the closed position toopen positions establishing fluid flow through the vent line means. Thecushion valve includes spring means 27 for resilient biasing the valveto the centered closed position. The cushion valve 26 has a pair ofactuating chambers 28,29 disposed at opposite ends 31,32 thereof.

A means 33 is provided for restricting fluid flow through the vent linemeans 22 when the cushion valve 26 is in the open position. The means 33in this embodiment is an orifice 34 disposed in the first section 23 ofthe vent line means 22. Alternatively, the orifice 34 can be positionedin the second section 24 of the vent line means 22 or internally withinthe cushion valve 26.

A flow restriction means 36 is disposed in the second motor conduit 18for generating a pressure differential in the fluid in the second motorconduit when fluid is flowing therethrough. The flow restriction means36 can be, for example, an orifice 37 disposed in the second motorconduit 18.

A means 38 is provided for moving the cushion valve 26 to theappropriate open position when the pressure differential in the fluid inthe second conduit 18 exceeds a predetermined level. The moving means 38includes a pair of pilot passages 39,41 connected to the actuatingchambers 28,29, respectively. The pilot passage 39 is connected to thesecond motor conduit 18 between the directional control valve and theorifice 37. The pilot passage 41 is connected to the second motorconduit between the motor 11 and the orifice 37.

A means 42 is provided for retaining the cushion valve 26 in the openposition for a predetermined limited time after the pressuredifferential drops below the preselected level. The means 42 includes apair of orifices 43,44 disposed in the pilot passages 39,41,respectively.

A second embodiment of the cushion swing circuit 10 of the presentinvention is disclosed in FIG. 2. It is noted that the same referencenumerals of the first embodiment are used to designate similarlyconstructed counterpart elements of this embodiment. In this embodiment,however, the flow restriction means 36 includes a pair of check valves46,47 arranged in parallel flow relationship between sections 18a,18b ofthe second motor conduit 18. Each of the check valves 46,47 includes aspring 48 which resiliently biases the respective check valve to theclosed position. The spring 48 establishes a pressure differential inthe motor conduit 18 at which the check valves open to permit flowtherethrough. In this embodiment, the pressure differential establishedby the check valves is substantially equivalent to the predeterminedlevel necessary for moving the cushion valve 26 to the open position.

Also in this embodiment a pilot vent passage 51 interconnects the pilotpassage 39 with the second portion 24 of the vent line means 22 throughan orifice 52. The orifice 52 is slightly larger than the orifice 43.

A third embodiment of the cushioned swing circuit 10 of the presentinvention is disclosed in FIG. 3. It is noted that the same referencenumerals of the first and second embodiments are used to designatesimilarly constructed counterpart elements of this embodiment. Thisembodiment, however, includes a pair of vent line means 56,57 and a pairof cushion valves 58,59 with the flow restriction means 36 including apair of orifices 60,61 individually disposed in the first and secondmotor conduits 17,18. The vent line means 56 has a first section 62connected to the first motor conduit 17 and a second section 63connected to the tank 16. Similarly, the second vent line means 57 has afirst section 62 connected to the second motor conduit 18 and a secondsection 63 connected to the tank 17. Each of the first sections 62 hasan orifice 34 therein.

The cushion valve 58 is disposed between and connected to the first andsecond sections 62,63 of the vent line means 56. Similarly, the cushionvalve 59 is disposed between and connected to the first and secondsections 62,63 of the vent line means 57. Each of the cushion valves58,59 is a two-position valve and is moveable between a closed positionas shown in the drawing and an open position. Each of the cushion valves58,59 include spring means 27 for resiliently biasing it to the closedposition and a pair of actuating chambers 28,29 at opposite endsthereof. Moreover, this embodiment includes a means 64 for moving thecushion valve 58 to the open position when a pressure differentialexceeding a predetermined level is generated in the second motor conduit18 when fluid is flowing therethrough from the directional control valve13 to the motors 11,12 and a means 66 for moving the cushion valve 59 tothe open position when a pressure differential exceeding a predeterminedlevel is generated in the first motor conduit 17 when fluid is flowingtherethrough from the directional control valve 18 to the motors 11,12.The moving means 64 includes a pilot passage 39 connected to theactuating chamber 28 of the cushion valve 58 and to the second motorconduit 18 between the directional control valve and the orifice 61 anda pilot passage 41 connected to the actuating chamber 29 of the cushionvalve 58 and to the second motor conduit 18 between the orifice 61 andthe hydraulic motor 11. Similarly, the moving means 66 includes a pilotpassage 67 connected to the actuating chamber 28 of the cushion valve 59and to the first motor conduit 17 between the directional control valve13 and the orifice 60 and a pilot passage 68 connected to the actuatingchamber 29 of the cushion valve 59 and the first motor conduit 17between the orifice 60 and the hydraulic motor 11. A means 69 forretaining the cushion valve 58 in the open position for a predeterminedlimited time after the pressure differential drops below thepredetermined level includes an orifice 71 disposed in the pilot passage39. Similarly, a means 70 for retaining the cushion valve 59 in the openposition for a predetermined limited time after the pressuredifferential in the first motor conduit 17 drops below the predeterminedlevel includes an orifice 72 disposed in the third pilot passage 67.

The pump 14 of the third embodiment is a variable displacement loadsensing pump and supplies fluid to the directional control valve 13 ofthe cushioned swing circuit 10 through a pressure compensated flowcontrol valve 73. The pressure compensated flow control valve 73 servesto maintain the pressure of the fluid delivered to the directionalcontrol valve 18 above a predetermined minimum pressure. The cushionedswing circuit 10 includes a replenishing means 74 for providing make-upthe fluid to the first and second motor conduits 17,18 when a negativepressure exists therein. The replenishing means 74 includes an orificedpassage 76 in the directional control valve with the orificed passagebeing connected to the first and second motor conduits 17,18 through apair of check valves 77,78.

Alternatively, the pump 14 of the first and second embodiments may alsobe a variable displacement load sensing pump. The predetermined level ofthe pressure differential can be, for example, in the range of fromabout 415 kPa to about 485 kPa.

Industrial Applicability

In the use of the present invention, simultaneous extension of thehydraulic motor 11 and retraction of the hydraulic motor 12 is initiatedby the operator shifting the directional control valve 13 upwardly tothe first operating position for directing pressurized fluid from thepump 14 into the second motor conduit 18 and communicating the firstmotor conduit 17 with the tank 16. As the fluid passes through theorifice 37, a pressure differential is generated in the second motorconduit 18 with the fluid pressure upstream of the orifice 37 beinggreater than the pressure downstream of the orifice. The upstreampressure is transmitted through the pilot passage 39 and the orifice 43into the actuating chamber 28 while the downstream pressure istransmitted through the pilot passage 41 and the orifice 44 into theactuating chamber 29. The pressure drop across the orifice 37 isresponsive to the flow rate through the second motor conduit 18 and oncethe pressure differential exceeds a predetermined level, the higherpressure in the actuating chamber 28 moves the cushion valve 26 to theright to the open position to establish fluid flow through the vent linemeans 23. While some of the pressurized fluid in the second motorconduit 18 passes through the vent line means 22 to the first motorconduit 17, the orifice 34 significantly restricts such flow so that ithas little effect on the operation of the circuit. The cushion valve 26will remain in the open position as described so long as sufficientfluid flow is passing through the orifice 37 to maintain the pressuredifferential above the predetermined level.

To stop the swinging motion of the mechanism controlled by the hydraulicmotors 11,12, the operator returns the directional control valve 13 tothe neutral position shown. This immediately blocks the pump 13 from thesecond motor conduit 18 and the first motor conduit 17 from the tank 16.However, the inertia energy of the mechanism will now cause inertiainduced pressurized fluid to be expelled from the hydraulic motors andinto the first conduit 17. The expelled fluid passes through the ventline means 22 and the orifice 34 therein, the cushion valve 26 andthrough the second motor conduit 18 into the motors 11,12 to dissipatethe inertia generated fluid pressure and maintain the motors filled withfluid. The orifice 34 restricts the fluid flow through the vent linemeans 22 and is sized to cause the hydraulic motors 11,12 tocontrollably coast to a stop. Simultaneously, with the above event, thestoppage of fluid flow through the second motor conduit 18 and theorifice 37 causes the pressure differential in the second motor conduit18 to drop below the predetermined level thereby allowing the springmeans 27 to start moving the cushion valve 26 toward the closedposition. However, the orifice 43 restricts the flow of fluid beingexpelled from the actuating chamber 28 and thereby retains the cushionvalve 26 in the open position for a predetermined limited time. The sizeof the orifice 43 is selected so that the predetermined limited timesubstantially coincides with the average time it takes the hydraulicmotors 11,12 to coast to a stop. The cushion valve will reach its closedposition at the end of the predetermined limited time so that thehydraulic motors are then hydraulically locked at the desired location.

Reverse motion of the hydraulic motors 11,12 is initiated by theoperator moving the directional control valve 13 downwardly to thesecond operating position. This causes pressurized fluid from the pump14 to cause retraction of the hydraulic motor 11 and extension of thehydraulic motor 12. The fluid expelled from the hydraulic motors passesthrough the second motor conduit 18, the orifice 37, and the directionalcontrol valve 13 to the tank 16. The flow of fluid through the orifice37 generates a pressure differential in the fluid upstream anddownstream thereof with the higher pressure fluid upstream thereof beingdirected through the pilot passage 41 and into the actuating chamber 29while the downstream pressure is transmitted through the pilot passage39 and into the actuating chamber 28. Thus, when pressure differentialexceeds the predetermined level, the cushion valve is moved to the leftagainst the bias of the spring means 27 to the open position toestablish communication through the vent line means 22. Thus, similarlyto that described above, when the directional control valve 13 is movedto the centered blocking position to stop movement of the hydraulicmotors 11,12, the cushion valve 26 is already open so that the fluidexpelled from the hydraulic motors due to the inertia energy in themechanism passes through the vent line means 22 and into the other endof the hydraulic motors. The cushion valve 26 will remain in the openposition for the predetermined limited time thereby allowing thehydraulic motors to controllably coast to a stop as dictated by theorifice 44.

The operation of the embodiment of FIG. 2 is essentially the same asdescribed above with the difference being the way the pressuredifferential in the second motor conduit 18 is generated. With thesecond embodiment, the pressure differential is generated by the flow offluid through the appropriate one of the check valves 46,47 dependingupon which direction the fluid is flowing. For example, when the fluidis flowing from the directional control valve 13 to the hydraulic motors11,12 through the motor conduit 18, the fluid passes through the checkvalve 46 such that the fluid pressure in the first section 18a will behigher than the fluid pressure in the second section 18b. The spring 49of check valve 46 establishes the pressure differential at apredetermined level which is sufficient to cause the cushion valve 26 tomove rightwardly to the first open position thereby establishing fluidcommunication through the vent line means 22. Similarly, when fluid isflowing through the second motor conduit 18 from the motors 11,12 to thedirection a control valve 13, the fluid passes through the check valve47 such that the fluid pressure in the second section 18b will be higherthan the fluid pressure in the first second 18a. The pressuredifferential in the motor conduit 18 will be established at apredetermined level by the spring 48 of the check valve 47 and will besufficient to cause the cushion valve 26 to move leftwardly to thesecond open position. As described above, the respective orifices 43,44will cause the cushion valve 26 to remain in the open position for apredetermined limited time after the fluid flow through the check valveshas stopped and the pressure differential drops below the predeterminedlevel so that the hydraulic motors controllably coast to a stop when thedirectional control valve 13 is moved from an operating position to ablocking position.

In the use of the embodiment of FIG. 3, when the directional controlvalve 13 is moved upwardly to the first operating position for directingfluid through the second motor conduit 18 to the hydraulic motors 11,12,the fluid flow through the orifice 61 generates a pressure differentialin the second motor conduit 18. The higher fluid pressure upstream ofthe orifice 61 is transmitted through the pilot passage 39 to theactuating chamber 28 of the cushion valve 58 while the lower downstreampressure is transmitted through the pilot passage 41 to the actuatingchamber 29. When the pressure differential exceeds the predeterminedlevel, the cushion valve 59 is moved rightwardly to the open position toestablish communication through the vent line means 56. Thus, when thedirectional control valve 13 is moved to the neutral closed position,the inertia generated fluid pressure in the first motor conduit 17 isdissipated through the vent line means 56 and the open cushion valve 58to the tank 16. Simultaneous therewith, the fluid replenishing system 74directs pressurized fluid through the orificed passage 76 and the checkvalve 78 in the directional control valve 13 and into the motor conduit18 to prevent cavitation from occurring in the hydraulic motors 11,12.Similar to that described above, the orifice 71 will delay movement ofthe cushion valve 58 to the closed position for the predeterminedlimited time after the pressure differential drops below thepredetermined level.

It should be noted that when the directional control valve 13 is in thefirst operating position described above, the fluid exhausted from thehydraulic motors 11,12 generates a pressure differential as it passesthrough the orifice 60 in the first motor conduit 17. However, since thehigher pressure is transmitted through the pilot passage 68 and into theactuating chamber 29 of the cushion valve 59, the cushion valve 59 isthereby biased toward the closed position so that communication throughthe vent line means 57 remains blocked.

Moving the directional control valve 13 downwardly to the secondoperating position results in the cushion valve 59 being moved to theopen position to establish communication through the vent line means 57and the cushion valve 59 to the tank 16. Thus, when the directionalcontrol valve is moved back to the neutral closed position, the inertiagenerated pressure in the second motor conduit 18 is dissipated throughthe vent line means 57 similarly to that described above.

The present invention provides an improved cushioned swing circuit inwhich a cushion valve is automatically moved to an open position toestablish communication through a vent line means during the normaloperation of the hydraulic motors and prior to inertia induced pressurebeing generated in the circuit. Thus, when inertia induced pressure isgenerated in the circuit, the pressure is dissipated through the ventline means allowing the implement controlled by the hydraulic motor tocontrollably coast to a stop. Movement of the cushion valve back to itsclosed position is delayed for a predetermined limited time whereuponthe cushion valve automatically moves to its closed position so that thehydraulic motors are then hydraulically locked in the desired position.

Other aspects, objects, and advantages of this invention can be obtainedfrom a study of the drawings, the disclosure, and the appended claims.

We claim:
 1. A cushioned swing circuit comprising:a bi-directionalhydraulic motor; a directional control valve; first and second conduitsindividually connected to the directional control valve and thehydraulic motor; vent line means connected to at least one of the firstand second motor conduits; a cushion valve connected to the vent linemeans and moveable between a closed position blocking fluid flow throughthe vent line means and an open position establishing fluid flow throughthe vent line means, said cushion valve including spring means forresiliently biasing the cushion valve to the closed position; means forrestricting fluid flow through the vent line means when the cushionvalve is in the open position; flow restriction means disposed in one ofthe first and second motor conduits for generating a pressuredifferential therein when fluid is flowing therethrough; means formoving the cushion valve to the open position position when the pressuredifferential exceeds a predetermined level; and means for retaining thecushion valve in the open position for a predetermined limited timeafter the pressure differential drops below the predetermined level. 2.The cushioned swing circuit of claim 1 wherein the vent line means isconnected to the first motor conduit and the flow restriction means isdisposed in the second motor conduit and generates said pressuredifferential therein when the fluid is flowing therethrough from thedirectional control valve to the hydraulic motor.
 3. The cushioned swingcircuit of claim 2 wherein the cushion valve has opposite ends and anactuating chamber at each of the ends, said moving means including afirst pilot passage connected to one of the actuating chambers and tothe second motor conduit between the directional control valve and theflow restriction means and a second pilot passage connected to the otherof the actuating chambers and to the second motor conduit between thehydraulic motor and the flow restriction means.
 4. The cushioned swingcircuit of claim 3 wherein the retaining means includes an orifice inthe first pilot passage.
 5. The cushioned swing circuit of claim 4wherein said flow restriction means includes an orifice disposed in thesecond motor conduit.
 6. The cushioned swing circuit of claim 5including a tank, said vent line means being in communication with thetank when the cushion valve is in the open position.
 7. The cushionedswing circuit of claim 6 including replenishing means for providingmake-up fluid to the second motor conduit when a negative pressureexists therein.
 8. The cushioned swing circuit of claim 6 includinganother vent line means connected to the second motor conduit and to thetank, another cushion valve connected to the another vent line means, anorifice in the another vent line means, a third pilot passage connectedto the first actuating chamber of the another cushion valve and to thefirst motor conduit between the directional control valve and theorifice, and a fourth pilot passage connected to the second actuatingchamber of the another cushion valve and to the first motor conduitbetween the hydraulic motor and the orifice, and an orifice in the thirdpilot passage.
 9. The cushioned swing circuit of claim 5 wherein thevent line means is connected to the second motor conduit and saidcushion valve is moveable to another open position at whichcommunication through the vent line means is established.
 10. Thecushioned swing circuit of claim 9 wherein said flow restriction meansgenerates a second pressure differential in the second motor conduitwhen fluid is flowing therethrough from the hydraulic motor to thedirectional control valve, said cushion valve being moved to anotheropen position when the second pressure differential exceeds saidpredetermined level.
 11. The cushioned swing circuit of claim 4 whereinthe flow restriction means includes a check valve disposed in the secondmotor conduit, said check valve being biased to a closed position by aspring.
 12. The cushioned swing circuit of claim 11 wherein the ventline means is connected to the second motor conduit and said cushionvalve is moveable to another open position at which communicationthrough the vent line means is established.
 13. The cushioned swingcircuit of claim 12 wherein said flow restriction means generates asecond pressure differential in the fluid in the second motor conduitwhen the fluid is flowing therethrough from the hydraulic motor to thedirectional control valve, said cushion valve being moved to the anotheropen position when the second pressure differential exceeds a secondpredetermined level.
 14. The cushioned swing circuit of claim 13 whereinsaid flow restriction means includes another check valve arranged inparallel flow relationship to the first mentioned check valve, saidanother check valve being biased to a closed position by a spring.